1. Field of the Invention
The present invention relates to a clamping device for a cylindrical shaft. More specifically, the invention relates to a clamping or locking device for restraining axial or rotatable movement of a cylindrical shaft.
2. Description of the Prior Art
The prior art is characterized by U.S. Pat. No. 4,577,732 and corresponding West German Patent Application No. 33 19 042. These devices are generally utilized for restraining a shaft as it is displaced longitudinally or rotatably. The clamping device is utilized to prevent movement of the shaft relative to the clamping unit. The activation force for the braking pressure is provided by a fluid introduced into the braking device. This fluid may be either air or hydraulic fluid. The device is specifically intended to permit both locking and unlocking of the shaft with relation to the housing.
U.S. Pat. No. 4,577,732 discloses a shaft which may be rotated or moved longitudinally within a braking housing. A series of ramped clamping elements are mounted adjacent the freely rotatably and longitudinally displaceable shaft. A series of ball or roller bearings are positioned on the ramp surfaces of the clamping devices and are designed to roll along the ramp surface. The ball or roller bearings are also in contact with a surface which is parallel to the surface of the rotatable shaft. This second surface is formed from the inner wall of a hollow piston. The second surface, the bearing and the ramped surface are positioned such that the bearing is rotated relative to the two surfaces by a movement of either. In this way, a displacement of the piston rolls the bearing along its inner wall and simultaneously rolls the bearing along the ramp surface of the clamping device. As the piston is unyielding, the bearing is urged against the ramped surface with increasing force as the bearing is displaced further along the ramp surface.
The ramp surface is designed to be flexible at one end, allowing slight displacement of the clamping means from its resting position. The clamping means is spaced at rest from the rotatable or axially displaceable shaft and urged by the bearing in contact with said shaft. Thus, the shaft is restrained from movement relative to the clamping means. The piston is displaced by fluid pressure in an adjacent chamber. The device illustrated in U.S. Pat. No. 4,577,732 is intended to be locked by increasing pressure in the fluid chamber and released by decreasing the pressure in the same chamber. The piston is moved from a locking to an unlocking position by the action of a spring. A restraining ring and a second spring are utilized to keep the bearing in registration with the two locking surfaces.
There are several limitations associated with the prior art device. The first such limitation is that the device which utilizes a specific cast or molded ramp clamping element is designed to be specifically fluid pressure activated. A second limitation is that the ramped clamping elements are integral to the shaft locking unit and require considerable time and effort to replace if worn or damaged. Relatedly, the use of a single roller or ball bearing with a single ramp surface contributes to premature wear or damage of the bearing surfaces.
There remains, therefore, a need in the art for a braking device which may easily be converted from a pressure actuated to a pressure released mechanism. Additionally, a device which utilizes easily replaceable bearing surfaces would require a minimum of repair time for replacement of the bearing surfaces. Lastly, a device is needed which minimizes the amount of wear on the bearings and the bearing surfaces to reduce the need for such repairs over time.